Crystalline color-conversion device

ABSTRACT

According to an embodiment, a crystalline color-conversion device includes an electrically driven first light emitter, for example a blue or ultraviolet LED, for emitting light having a first energy in response to an electrical signal. An inorganic solid single-crystal direct-bandgap second light emitter having a bandgap of a second energy less than the first energy is provided in association with the first light emitter. The second light emitter is electrically isolated from, located in optical association with, and physically connected to the first light emitter so that in response to the electrical signal the first light emitter emits first light that is absorbed by the second light emitter and the second light emitter emits second light having a lower energy than the first energy.

PRIORITY APPLICATION

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 62/173,200, filed Jun. 9, 2015, titled“Crystalline Color-Conversion Device,” the content of which isincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to light-emitting structures using anelectrically driven light emitter to optically pump an inorganic solidsingle-crystal direct-bandgap light emitter.

BACKGROUND OF THE INVENTION

Solid-state electrically controlled light emitters are widely used inthe display and lighting industries. Displays often use differentlycolored emitters, and lighting applications require a large colorrendering index (CRI). In either case, the efficient production of avariety of colors is important.

Colored light is produced in liquid crystal displays (LCDs) and someorganic light-emitting diode (OLED) displays using white-light emitters(such as a backlight) and color filters, for example as taught in U.S.Pat. No. 6,392,340. However, this approach has the disadvantage ofwasting much of the white light produced by the back light. In adifferent approach, light emitters emit a specific desired color. Forexample, some OLED displays use different organic materials to emitlight of different colors. This design requires the patterneddistribution of the different organic materials over a display substrateat a micron-level resolution, for example using evaporation through amechanical shadow mask. However, it is difficult to maintain patternaccuracy using metal shadow masks over large display substrates, forexample greater than 300 mm by 400 mm, or display substrates requiringhigh resolution.

Inorganic light-emitting diodes (LEDs) based on crystallinesemiconductor materials are also used to emit light of differentfrequencies. These crystalline-based inorganic LEDs provide highbrightness, excellent color saturation, long lifetimes, goodenvironmental stability, and do not require expensive encapsulation fordevice operation, especially in comparison to OLEDs. However, thecrystalline semiconductor layers also have a number of disadvantages.For example, crystalline-based inorganic LEDs have high manufacturingcosts, difficulty in combining multi-color output from the same chip,low efficiency, color variability and poor electrical current response.

Most solid-state lighting products desirably emit white light with alarge color rendering index, for example greater than 80 or even 90.Since solid-state light emitters emit colored rather than white light,multiple different colored solid-state light emitters are often used toprovide the appearance of white light. For example, LED backlights inLCDs, or white OLED emitters in some OLED displays, use a combination ofblue and yellow emitters or red, green, and blue emitters that togetherare experienced as white light by the human visual system. However, thistechnique requires the use of different light emitters that emitdifferent colors of light. As noted above, different light emitters havedifferent electrical and colorimetric properties leading to inefficiencyand non-uniformity.

Another technique used to provide colored light is color conversion, inwhich a single kind of light emitter is used to optically stimulate(pump) a second light emitter with light having a first energy(frequency). The second light emitter absorbs the first light and thenemits second light having a lower energy (frequency). By choosing avariety of different second light emitters that emit light of differentfrequencies, a display or a solid-state light device can emit light ofdifferent colors. For example, a blue light emitter can be used to emitblue light and to optically pump yellow, red, or green light emitters.U.S. Pat. No. 7,990,058 describes an OLED device with a color-conversionmaterial layer.

Phosphors are often used as color-conversion materials. For example,U.S. Pat. No. 8,450,927 describes an LED lamp using a phosphor and U.S.Pat. No. 7,969,085 discloses a color-change material layer that convertslight of a second frequency range higher than a first frequency range tolight of the first frequency range. Light-emissive inorganic core/shellnano-particles (quantum dots or QDs) are also used to produce opticallypumped or electrically stimulated colored light, for example as taughtin U.S. Pat. No. 7,919,342.

In general, color-change material systems suffer from efficiencyproblems. For example, the production of relatively higher-frequencyblue light can be difficult and the conversion of light from relativelyhigher frequencies to relatively lower frequencies may not be efficient.Moreover, the conversion materials may fade over time, reducing theperformance of the display. Furthermore, much of the relativelyhigher-frequency light may not interact with the color-change materialsand thus may not be converted to the desired, relatively lower frequencylight. U.S. Patent Publication 2005/0140275A1 describes the use of red,green, and blue conversion layers for converting white light into threeprimary colors of red, green, and blue light. However, the efficiency ofemitted-light conversion remains a problem.

Diode-pumped solid-state lasers use a solid gain medium such as aneodymium-doped yttrium aluminum garnet crystal. Light from one or morelight-emitting diodes is imaged with a lens or optical fiber onto one ormore sides of the crystal. The crystal then lases to produce coherentlight.

Inorganic displays use arrays of inorganic light emitters, typicallylight-emitting diodes (LEDs). Because of the variability in LEDmaterials and manufacturing processes, different LEDs, even when made insimilar materials, will have different performances and losses in thecircuits providing power to the different LEDs. LEDs made in differentmaterials have even greater inefficiencies when provided with a commonpower source. Furthermore, these issues are exacerbated in LEDs sincethe variability of materials in a source semiconductor wafer is muchgreater on a smaller scale than on a larger scale. These differenceslead to performance inefficiency and uniformity variations.

Although a variety of devices produce arrays of emitters emittingdifferent colors of light, there remains a need for structures andmethods that improve power efficiency and performance uniformity in theproduction of colored light in a simple and robust structure made withfewer parts.

SUMMARY OF THE INVENTION

The present invention provides a light-emitting structure and displaywith improved optical efficiency, highly saturated colored light, andimproved electrical efficiency. Embodiments of the present inventionalso enable robust methods of manufacturing.

According to an embodiment, a crystalline color-conversion deviceincludes an electrically driven first light emitter, for example a blueor ultraviolet LED, for emitting light having a first energy in responseto an electrical signal. An inorganic solid single-crystaldirect-bandgap second light emitter having a bandgap of a second energyless than the first energy is provided in association with the firstlight emitter. The second light emitter is electrically isolated from,located in optical association with, and located within 0 to 250 micronsof the first light emitter so that in response to the electrical signalthe first light emitter emits light that is absorbed by the second lightemitter and the second light emitter emits light of a lower energy thanthe first light emitter. Different single-crystal direct-bandgap lightemitters emit different colors of light. Arrays of the differentcrystalline color-conversion devices of the present invention canprovide a multi-color pixel display. The first and second light emitterscan be in physical contact, i.e. touching, or can be separated by anadhesive layer adhering the first light emitter to the second lightemitter, forming a solid-state crystalline color-conversion device.

Crystalline LEDs are efficient light emitters and direct-bandgapcrystals efficiently absorb and transmit light. Closely locating the LEDto the direct bandgap crystals provides an efficient, solid-stateoptical structure with few losses in an environmentally and mechanicallyrobust device. Such a structure is also amenable to micro-transferprinting enabling an efficient and low-cost manufacturing method fordisplay devices using the crystalline color-conversion device of thepresent invention.

In one aspect, the disclosed technology includes a crystallinecolor-conversion device, including: an electrically driven first lightemitter for emitting first light having a first energy in response to anelectrical signal; and an inorganic solid single-crystal direct-bandgapsecond light emitter having a bandgap of a second energy less than thefirst energy, wherein the second light emitter is electrically isolatedfrom the first light emitter, is located in optical association with thefirst light emitter, and is located within 0 to 250 microns of the firstlight emitter so that in response to the electrical signal the firstlight emitter emits first light that is absorbed by the second lightemitter and the second light emitter emits second light having a lowerenergy than the first energy.

In certain embodiments, the second light emitter has a compositiondifferent from the first light emitter.

In certain embodiments, the first light emitter is an inorganic solidsingle-crystal direct bandgap light emitter.

In certain embodiments, the crystal lattice structure of the first lightemitter is different from the crystal lattice structure of the secondlight emitter.

In certain embodiments, the first light emitter is a light-emittingdiode, a laser, or a vertical-cavity surface-emitting laser (VCSEL).

In certain embodiments, the first light emitter is in physical contactwith the second light emitter.

In certain embodiments, the device includes a material that is at leastpartially transparent to the color of light emitted by the first lightemitter and is located between and in contact with the first lightemitter and the second light emitter.

In certain embodiments, the material is plastic, is an adhesive, is acurable adhesive, is a resin, or is a curable resin, or wherein thematerial is a dielectric stack that is an optical filter.

In certain embodiments, the second light emitter is at least one ofInGaN, bulk or quasi-bulk InGaN, InGaP, InGaAl phosphide, devoid ofarsenic, devoid of cadmium, and devoid of rare earths.

In certain embodiments, the second light emitter emits second light thathas a peak wavelength of 460 nm or less.

In certain embodiments, the device includes a plurality of first lightemitters and a corresponding plurality of second light emitters.

In certain embodiments, each of the plurality of first light emittershas a common material and crystal lattice structure.

In certain embodiments, each of the plurality of first light emittersemits blue or ultraviolet first light.

In certain embodiments, at least some of the plurality of second lightemitters are different from others of the plurality of second lightemitters.

In certain embodiments, at least one of the plurality of second lightemitters emits second light that is red, green, blue, or infrared.

In certain embodiments, at least a first one of the plurality of secondlight emitters emits red light, a second one of the plurality of secondlight emitters emits green light, and a third one of the plurality ofsecond light emitters emits blue light.

In certain embodiments, the first light emitter emits white light.

In certain embodiments, the first light emitter emits a third light of athird energy less than the second energy and the third light passesthrough the second light emitter.

In certain embodiments, the second light emitter comprises at least oneof surface passivation, atomic layer deposition surface passivation,light out-coupling structure, light-extraction structures, templatedepitaxial structures, and holes.

In certain embodiments, the second light emitter has a thickness largeenough to convert substantially all incident first light from the firstlight emitter having an energy greater than the second energy to lightof the second energy.

In certain embodiments, the second light emitter has a thickness chosento convert a pre-determined fraction of the incident first light havingan energy greater than the second energy to light of the second energy.

In certain embodiments, the device includes an inorganic solidsingle-crystal direct-bandgap third light emitter having a bandgap of athird energy less than the first energy, the third light emitter locatedon a side of the second light emitter opposite the first light emitter.

In certain embodiments, the second light emitter has at least a firstportion having a first thickness and a second portion having a secondthickness less than the first thickness, the first thickness largeenough to convert substantially all incident first light having anenergy greater than the second energy to light of the second energy andthe second thickness small enough that a substantial amount of incidentfirst light having an energy greater than the second energy is notconverted to light of the second energy.

In certain embodiments, the second light emitter comprises a cavity inwhich the first light emitter is disposed.

In certain embodiments, the second light emitter comprises inorganicdirect-bandgap crystals that are disposed on multiple sides of the firstlight emitter to partially surround the first light emitter.

In certain embodiments, the device includes a plurality of first lightemitters in optical association with the second light emitter.

In certain embodiments, the device includes an inorganic solidsingle-crystal direct-bandgap third light emitter having a bandgap of athird energy less than the first energy and that is electricallyisolated from the first light emitter.

In certain embodiments, the third light emitter is located in opticalassociation with the first light emitter and is located within 0 to 250microns of the first light emitter so that in response to the electricalsignal the first light emitter emits first light that is absorbed by thethird light emitter and the third light emitter emits third light havinga lower energy than the first energy.

In certain embodiments, the third light emitter has a bandgap of a thirdenergy less than the second energy, the third light emitter is locatedin optical association with the second light emitter, and is locatedwithin 0 to 250 microns of the second light emitter so that lightemitted by the second light emitter is absorbed by the third lightemitter and the third light emitter emits third light having a lowerenergy than the second energy.

In certain embodiments, the device includes a reflective layer locatedat least partially over the first light emitter or the second lightemitter, or both the first light emitter and the second light emitter,that reflects light emitted by the first or second light emitters inundesirable directions.

In certain embodiments, the second light emitter is an optically pumpedlaser.

In certain embodiments, the second light emitter includes alight-extraction structure.

In certain embodiments, the device includes an electrically connectedelectrostatic gate formed on, under, or over a near-edge region of thesecond light emitter.

In certain embodiments, the second light emitter is a semiconductorheterostructure comprising two different semiconductor materials orstructures.

In certain embodiments, the semiconductor heterostructure has a claddinglayer at least partially surrounding an active photoluminescent layer,the cladding layer having an energy bandgap larger than the energybandgap of the active photoluminescent layer.

In certain embodiments, the cladding layer has an energy bandgap largerthan the energy bandgap of the first emitter or wherein the claddinglayer has an energy bandgap equal to or less than the energy bandgap ofthe first emitter and a thickness that is less than the thickness of thephotoluminescent layer.

In certain embodiments, the second light emitter is less than or equalto two microns thick.

In certain embodiments, the second light has a full width half max(FWHM) less than or equal to 50 nm.

In certain embodiments, at least one of the first light emitter andsecond light emitter has a width from 2 to 5 μm, 5 to 10 μm, 10 to 20μm, or 20 to 50 μm.

In certain embodiments, at least one of the first light emitter andsecond light emitter has a length from 2 to 5 μm, 5 to 10 μm, 10 to 20μm, or 20 to 50 μm.

In certain embodiments, at least one of the first light emitter andsecond light emitter has with a height from 2 to 5 μm, 4 to 10 μm, 10 to20 μm, or 20 to 50 μm.

In certain embodiments, the device includes an optical filter disposedon a side of the second light emitter opposite the first light emitterto reflect light from the first light emitter and transmit light emittedfrom the second light emitter.

In another aspect, the disclosed technology includes a crystallinecolor-conversion display, the display including: a display substrate;and the plurality of first light emitters and corresponding plurality ofsecond light emitters located on or over the display substrate anddistributed over the display substrate.

In certain embodiments, the plurality of second light emitters aregrouped into pixel groups, each pixel group including at least a redsecond light emitter emitting red light, a green second light emitteremitting green light, and a blue second light emitter emitting bluelight.

In certain embodiments, each of the plurality of first light emittershas a common material and crystal lattice structure.

In certain embodiments, the second light emitters are located betweenthe first light emitters and the display substrate and the second lightemitters emit light through the display substrate.

In certain embodiments, the first light emitters are located between thesecond light emitters and the display substrate and the second lightemitters emit light in a direction opposite the display substrate.

In certain embodiments, the display substrate is a member selected fromthe group consisting of polymer, plastic, resin, polyimide, polyethylenenaphthalate, polyethylene terephthalate, metal, metal foil, glass, asemiconductor, and sapphire.

In certain embodiments, the display substrate has a transparency greaterthan or equal to 50%, 80%, 90%, or 95% for visible light.

In another aspect, the disclosed technology includes a method of makinga crystalline color-conversion device, including: providing anelectrically driven first light emitter for emitting first light havinga first energy in response to an electrical signal; providing aninorganic solid single-crystal direct-bandgap second light emitterhaving a bandgap of a second energy less than the first energy; andmicro transfer printing the second light emitter onto the first lightemitter or micro transfer printing the first light emitter onto thesecond light emitter, wherein the second light emitter is electricallyisolated from the first light emitter, is located in optical associationwith the first light emitter, and is located within 0 to 250 microns ofthe first light emitter so that in response to the electrical signal thefirst light emitter emits first light that is absorbed by the secondlight emitter and the second light emitter emits second light having alower energy than the first energy.

In certain embodiments, the first and second light emitters form alight-emitting conversion structure and comprising micro-transferprinting the light-emitting conversion structure onto a displaysubstrate.

In certain embodiments, the method includes forming an inorganic solidsingle-crystal direct-bandgap layer on a source substrate and disposingthe first light emitters onto the layer.

In certain embodiments, the method includes etching the layer to form aplurality of spatially separated crystalline color-conversion devices onthe source substrate.

In certain embodiments, the method includes micro transfer printing thecrystalline color-conversion devices from the source substrate to adisplay substrate.

In certain embodiments, the method includes providing an inorganic solidsingle-crystal direct-bandgap source substrate and disposing the firstlight emitters onto the layer.

In certain embodiments, the method includes etching the layer to form aplurality of spatially separated crystalline color-conversion devices.

In certain embodiments, the method includes micro transfer printing thecrystalline color-conversion devices from the source substrate to adisplay substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, features, and advantages ofthe present disclosure will become more apparent and better understoodby referring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective of an embodiment of the present invention;

FIG. 2 is a cross section of a bottom-emitter embodiment of the presentinvention;

FIG. 3 is a cross section of an LED structure in accordance withembodiments of the present invention;

FIG. 4 is a cross section of another embodiment of the present inventionhaving additional material layers;

FIG. 5 is a perspective of an embodiment of the present invention havingan array of crystalline color-conversion devices;

FIG. 6 is a cross section of a top-emitter embodiment of the presentinvention;

FIG. 7 is a cross section of a structure in accordance with embodimentsof the present invention;

FIG. 8 is a cross section according to another embodiment of the presentinvention having three light emitters;

FIG. 9 is a cross section of a structured light emitter according to anembodiment of the present invention;

FIG. 10 is a cross section of an embodiment of the present inventionincluding electrostatic gates;

FIG. 11 is a cross section of an embodiment of the present inventionincluding a heterostructure second light emitter; and

FIGS. 12-13 are flow charts illustrating methods of the presentinvention.

The features and advantages of the present disclosure will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The figures are not drawn to scalesince the variation in size of various elements in the Figures is toogreat to permit depiction to scale.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, in an embodiment of the present invention acrystalline color-conversion device 5 includes an electrically drivenfirst light emitter 10 for emitting light having a first energy inresponse to an electrical signal, for example from a controller (notshown), from a light-emitting area 11 within the first light emitter 10.An inorganic solid single-crystal direct-bandgap second light emitter 20having a bandgap of a second energy less than the first energy iselectrically isolated from the first light emitter 10, is located inoptical association with the first light emitter 10, and is locatedwithin 0 to 250 microns of the first light emitter 10 so that inresponse to the electrical signal the first light emitter 10 emits firstlight that is absorbed by the second light emitter 20 and the secondlight emitter 20 emits second light having a lower energy than the firstenergy.

As used herein, “in optical association” means that light from the firstlight emitter 10 is incident upon the second light emitter 20.

As used herein “located within 0 to 250 microns” means that the firstlight emitter 10 can be in contact with the second light emitter 20 orwithin, for example, 10, 20, 50, 100, 200, or 250 microns of the secondlight emitter 20 such that the first light emitter 10 and the secondlight emitter 20 are separated by a distance from 0 to 250 microns,inclusive. In an embodiment in which the first light emitter 10 isseparated from the second light emitter 20, the first light emitter 10can be adhered to the second light emitter 20 by a thin, transparentadhesive layer. The thin, transparent adhesive layer can have a variablethickness but in any case serves to adhere the first light emitter 10 tothe second light emitter 20 without undue absorption of light (e.g.,adhesive layer is 80-100% transparent to visible or emitted light), forexample the first light emitted by the first light emitter 10.

As illustrated in FIG. 1, the crystalline color-conversion device 5 canbe mounted on a substrate 30. The substrate 30 can be a transparentsubstrate 30 that is substantially transparent to the light emitted bythe first or second light emitters 10, 20, for example 50%, 70%, 80%,90%, or 95% transparent. The substrate 30 can be a polymer, plastic,resin, polyimide, PEN, PET, metal, metal foil, glass, a semiconductor,or sapphire.

In various embodiments, the first light emitter 10 can be, for example,a light-emitting diode, a laser, a diode laser, or a vertical cavitysurface emitting laser and can include known light-emitting diodematerials and structures. The first light emitter 10 can also be aninorganic solid single-crystal direct bandgap light emitter. The firstlight emitter 10 can emit blue, violet, or ultra-violet light, and canemit either coherent or incoherent light. The light emitters used hereincan have at least one of a width, length, and height from 2 to 5 μm, 4to 10 μm, 10 to 20 μm, or 20 to 50 μm.

In some embodiments, the second light emitter 20 is a crystal, asemiconductor crystal, or a doped semiconductor crystal. Dopants caninclude neodymium, chromium, erbium or ytterbium. The second lightemitter 20 can include InGaN, bulk or quasi-bulk InGaN, InGaP, InGaAlphosphide, yttrium aluminum garnet, yttrium orthovanadate, beta bariumborate, lithium triborate, bismuth triborate, or potassium titanylphosphate. The second light emitters 20 can be devoid of arsenic,cadmium, or rare earths. The second light emitter 20 can be an opticallypumped laser. In an embodiment, the second light emitter 20 emits secondlight that has a peak wavelength of 460 nm or less or emits red, yellow,green, cyan, or blue light. Because the second light emitted from thesecond light emitter 20 can be a very pure light and highly saturated,the second light can have a full width half max (FWHM) less than orequal to 50 nm or even less than or equal to 20 nm. Single-crystaldirect bandgap semiconductor light emitters can be very efficient atboth absorbing incident first light and effective at emitting lowerfrequency light. Hence, in an embodiment, the second light emitter isless than or equal to two microns thick, or even less than or equal toone micron thick.

In an embodiment of the present invention, the second light emitter 20has a composition different from the first light emitter 10. The crystallattice structure of the first light emitter 10 can be different fromthe crystal lattice structure of the second light emitter 20. The secondlight emitter 20 can include surface passivation and light out-couplingstructures. The surface passivation can be provided, for example, usingatomic layer deposition (ALD) and can be only one or a few atoms thick.In embodiments, the refractive index of the second light emitter 20 ismuch greater than the refractive index of air and the use of lightout-coupling or light-extraction structures can facilitate efficientlight emission and reduce total internal reflection and heating.

Referring to FIG. 2, a structure of the present invention includes afirst light emitter 10 located within 0 to 250 microns of the secondlight emitter 20, for example in physical contact with the second lightemitter 20 as shown. The second light emitter 20 is mounted on thesubstrate 30. In this embodiment, the first light emitter 10 is an LEDformed with electrical contacts 14 on a side of the LED opposite thesecond light emitter 20. The electrical contacts 14 are electricallyconnected to conductive wires 18 insulated from the first light-emitter10 by a dielectric 16. The electrical contacts 14 are driven by controlsignals, for example from an external controller (not shown), to controlthe LED to emit first light 60 having the first energy. The first light60 is absorbed by the second light emitter 20 and the second lightemitter 20 emits second light 62 that passes through the substrate 30and can be viewed by an observer. Thus, the first light emitter 10optically pumps the second light emitter 20. In an embodiment, areflector 15 is located over the gap between the electrical contacts 14and is electrically insulated from the electrical contacts 14 by thedielectric 16. In a further embodiment, a reflective layer (e.g., metal)is disposed at least partially over the second light emitter 20 toreflect light emitted by the first or second light emitters 10, 20 inundesirable directions.

As shown in the embodiment of FIGS. 3 and 4, the first light emitter 10is formed in layers, for example including a conduction layer 13including a transparent doped semiconductor layer, to which is connectedan electrical contact 14. The conduction layer 13 efficiently conductscurrent without emitting light to a light-emitting layer 12 that is alsoconnected to an electrical contact 14. Electrical current flowingthrough the light-emitting layer 12 causes the light-emitting layer 12to emit first light 60. The light-emitting layer 12 can also includemultiple doped semiconductor sub-layers, for example n- and p-dopedsub-layers doped in different amounts or with different dopants.

The second light emitter 20 is located in optical association with andis physically located within 0 to 250 microns of the first light emitter10. In the embodiment illustrated in FIGS. 1 and 2, the first lightemitter 10 is within 0 microns of the second light emitter 20 so thatthe first light emitter 10 is in physical contact with and touches thesecond light emitter 20. In such an embodiment, the first and secondlight-emitters 10 and 20 are not separated by a vacuum or a gas and forma solid-state structure. In yet another embodiment of the crystallinecolor-conversion device 5 illustrated in FIG. 4, a material 22 that isat least partially transparent (for example 50%, 70%, 80%, 90%, 95%, or100%) to the color of light emitted by the first light emitter 10 islocated between and in physical contact with the first light emitter 10and the second light emitter 20. The material 22 can be an adhesive, acurable adhesive, a resin, or a curable resin. In an embodiment, thematerial 22 is an optically clear adhesive (OCA). In a furtherembodiment and as shown in FIG. 4, the material 22 is also locatedbetween the second light emitter and the substrate 30.

In an embodiment, the material 22 is formed in a layer that issubstantially planar, is index matched to either or both of the firstand second light emitters 10, 20, or does not change the direction ofthe first light 60 emitted from the first light emitter 10. In anotherembodiment, the material 22 does not form a lens or demonstrate totalinternal reflection or have a graded index through the layer of material22. In a further embodiment, the material 22 layer includes sub-layersforming a dielectric stack. The sub-layers can have different oralternating refractive indices and can be selected to form an opticalfilter that transmits light emitted light from the first light emitter10 but reflects light from the second light emitter 20, therebyimproving the conversion and light output efficiency of the crystallinecolor-conversion device 5. Alternatively, one or more layers overlyingboth the first and second light emitters 10, 20, for example thedielectric insulator 16, serve to hold the first and second lightemitters 10, 20 together. In an additional embodiment, an optical filterthat can be a dielectric stack is disposed on a side of the second lightemitter 20 opposite the first light emitter 10 that reflects light fromthe first light emitter 10 and transmits light emitted from the secondlight emitter 20.

In another embodiment of the present invention, the second light emitter20 incorporates a cavity such as a pocket, receptacle, recess, orhollowed-out portion into which the first light emitter 10 is disposed.The cavity serves as both a mechanical alignment feature when disposingthe first light emitter 10 in optical association with the second lightemitter 20 or when disposing the second light emitter 20 in opticalassociation with the first light emitter 10. Locating the first lightemitter 10 in the cavity of the second light emitter 20 also enables thesecond light emitter 20 to partially surround the first light emitter10, so that more light emitted from the first light emitter 10 isconverted by the second light emitter 20.

In yet another embodiment of the present invention, the second lightemitter 20 includes multiple inorganic direct-bandgap crystals that aredisposed on multiple sides of the first light emitter 10 to partiallysurround the first light emitter 10, so that more light emitted from thefirst light emitter 10 is converted by the second light emitter 20. Themultiple inorganic direct-bandgap crystals can be identical ordifferent, or can have the same thickness or have different thicknesses.The different materials or sizes can produce light of differentfrequencies.

Alternatively, multiple first light emitters 10 are located in opticalassociation with a single second light emitter 20 so that light emittedby the first light emitters 10 is converted by the single second lightemitter 20. The multiple first light emitters 10 can be identical ordifferent, for example including different materials or having differentsizes or are driven with different signals or at different time. Suchstructural alternatives can have mechanical advantages in alignment ordisposition of the first and second light emitters 10, 20, improvedlight conversion efficiency, improved CRI, less flicker, increased poweror light emitted from a single crystalline color-conversion device 5, orreduced costs in manufacturing. Such arrangements can also reducefailures if, for example either a second light emitter 20 fails or afirst light emitter 10 fails.

Referring next to FIG. 5, a crystalline color-conversion display 7includes a plurality of the crystalline color-conversion devices 5located on a display substrate 30, each having a first light emitter 10and a corresponding second light emitter 20. The plurality ofcrystalline color-conversion devices 5 are distributed over or on thedisplay substrate 30, for example in an array. Groups 40 of thecrystalline color-conversion devices 5 including the first and secondlight emitters 10, 20 can form pixels or sub-pixels in the crystallinecolor-conversion display 7. Each of the plurality of first lightemitters 10 can be the same kind of light emitter and have a commonmaterial and crystal lattice structure so that they have similaroperating characteristics and can be provided and located on thesubstrate 30 in a common step. In a further embodiment, at least some ofthe second light emitters 20 are different from other second lightemitters 20, for example so that they emit different colors of light.For example, at least one of the plurality of second light emitters 20can emit red light, another one of the second light emitters 20 can emitgreen light, and a third one of the second light emitters 20 can emitblue light so that the crystalline color-conversion display 7 includescrystalline color-conversion devices 5R emitting red light, crystallinecolor-conversion devices 5G emitting green light, and crystallinecolor-conversion devices 5B emitting blue light. In another embodiment,at least one of the plurality of second light emitters 20 emits infraredlight. Pixel groups 40 can include one each of the crystallinecolor-conversion devices 5R, 5G, and 5B to form multi-color pixels inthe crystalline color-conversion display 7.

In the embodiment illustrated in FIG. 2 the second light emitter 20 isbetween the substrate 30 and the first light emitter 10 and emits lightthrough the substrate 30 in a bottom-emitter configuration. In analternative top-emitter configuration illustrated in FIG. 6, the firstlight emitter 10 is located between the substrate 30 and the secondlight emitter 20. As shown in FIG. 6, the conductive wires 18 can beformed on the substrate 30 and the first light emitter 10 located overthe patterned conductive wires 18 to electrically connect the electricalcontacts 14 to the conductive wires 18. The electrical contacts 14 havedifferent thicknesses to facilitate electrical connections from theelectrical contacts to the patterned conductive wires on the substrate30. The dielectric 16 protects and insulates the structure. The secondlight emitter 20 is in contact with the first light emitter 10 and, asshown in FIG. 7, when stimulated by a current supplied through theelectrical contacts 14, the first light emitter 10 emits first light 60at least a portion of which is absorbed by the second light emitter 20.In response to the first light 60, the second light emitter 20 emitssecond light 62.

In a further embodiment of the present invention, the first lightemitter 10 emits white light, for example a white-light LED. Suchsolid-state white-light emitters typically emit at least two differentcolors, for example blue and yellow, and can themselves includecolor-change materials, such as phosphors. Thus, in such an embodimentthe first light emitter 10 also emits third light of a third energy lessthan the second energy and the light of the third energy passes throughthe second light emitter 20. As illustrated in FIG. 7, low-energy pumplight 61 emitted from the first light emitter 10 passes through thesecond light emitter 20 and can be viewed by an observer. Higher-energylight (first light 60) can be absorbed by the second light emitter 20and is emitted as a lower energy light (second light 62 having thesecond energy). Using this method, a wider variety of colors can beformed or the use of expensive or hard-to-find single-crystaldirect-bandgap materials avoided.

In an embodiment of the present invention, the second light emitter 20has a thickness large enough to convert substantially all incident lighthaving an energy greater than the second energy, for example from thefirst light emitter 10, to light of the second energy. In anotherembodiment, the second light emitter 20 has a thickness chosen toconvert a pre-determined fraction of the incident light having an energygreater than the second energy, for example first energy light from thefirst light emitter 10, to light of the second energy. Thus, lighthaving a pre-determined combination of different colors (the firstenergy light and the second energy light) is emitted.

In alternative embodiments, the second light emitters 20 have avariation in thickness, for example made with templated epitaxialstructures, or holes, using photolithographic methods. This variablethickness can result in multi-color light output. In such an embodiment,illustrated in FIG. 8, the second light emitter 20 has at least a firstportion having a first thickness T1 and a second portion having a secondthickness T2 less than the first thickness T1. The first thickness T1 islarge enough to convert substantially all incident light (e.g. Firstlight 60 emitted from the first light emitter 10) having an energygreater than the second energy to light of the second energy (secondlight 62). The second thickness T2 is small enough that a substantialamount of incident light (e.g. First light 60) having an energy greaterthan the second energy is not converted to light of the second energyand is emitted directly from the second light emitter 20, as shown.Again, light having a pre-determined combination of different colors(the first energy light and the second energy light) is emitted. Inanother embodiment of the present invention, the second light emitter 20includes a light-extraction structure on or in a surface of the secondlight emitter 20 to reduce the quantity of trapped light in the secondlight emitter. Such structured second light emitters 20 can be madephotolithographically.

Referring to FIG. 9, in an alternative structure according to thepresent invention, the crystalline color-conversion device 5 includes aninorganic solid single-crystal direct-bandgap third light emitter 28having a bandgap of a third energy less than the first energy and thatis electrically isolated from the first light emitter 10. In oneembodiment, the third light emitter 28 is located in optical associationwith the first light emitter 10 and is located within 0 to 250 micronsof the first light emitter 10 so that in response to the electricalsignal the first light emitter 10 emits first light that is absorbed bythe third light emitter 28 and the third light emitter 28 emits thirdlight having a lower energy than the first energy. The third lightemitter can receive light emitted directly from the first light emitter10 without passing through the second light emitter 20 (not shown). Inanother embodiment, the third light emitter 28 has a bandgap of a thirdenergy less than the second energy, the third light emitter 28 islocated in optical association with the second light emitter 20, andthird light emitter 28 is located within 0 to 250 microns of the secondlight emitter 20 so that light emitted by the second light emitter 20 isabsorbed by the third light emitter 28 and the third light emitter 28emits third light having a lower energy than the second energy. Byemploying a third light emitter 28 in various structural arrangements, abroader range of frequencies are emitted by the crystallinecolor-conversion device 5, providing improved CRI.

As shown in FIG. 9, in an embodiment of the crystalline color-conversiondevice 5 of the present invention, an inorganic solid single-crystaldirect-bandgap third light emitter 28 having a bandgap of a third energyless than the first energy is located on a side of the second lightemitter 20 opposite the first light emitter 10. Various combinations ofbandgap energies in the first, second, and third light emitters 10, 20,28 and different thicknesses of the second and third light emitters 20,28 can result in different combinations and quantities of light emittedfrom the structure. In one embodiment, at least a portion of the secondlight 62 emitted by the second light emitter 20 in response to the firstlight 60 from the first light emitter 10 is converted by the third lightemitter 28 to third light 64A. In another embodiment, at least a portionof the first light 60 from the first light emitter 10 passes through thesecond light emitter 20 and is converted by the third light emitter 28and emitted as third light 64B. In another embodiment, at least aportion of the first light 60 is converted by the second light emitter20 and passes through the third light emitter 28 and is emitted assecond light 62A.

Referring next to FIG. 10, in an embodiment of the present invention thecrystalline color-conversion device 5 includes electrostatic gates 17located on, over, under, or adjacent to near-edge regions of the secondlight emitter 20. In embodiments, the electrostatic gate 17 can be incontact with the second light emitter 20 or separated from the secondlight emitter by the dielectric 18. By placing a charge on theelectrostatic gates 17, an electrical field is formed in the secondlight-emitter 20 that depletes carriers in the near-edge regions,thereby reducing non-radiative recombination. In an embodiment, theelectrostatic gates 17 are electrically connected to one of theconductive wires 18 or, alternatively, the electrostatic gates 17 areelectrically connected to a different charge source. Electrostatic gates17 can be formed on the second light emitter 20 using photolithographicmethods.

As noted above, the second light emitter 20 can be a semiconductor.Referring to FIG. 11, in an embodiment the second light emitter 20 is aheterostructure 70 including two different semiconductor materials ortwo different semiconductor structures. Such a heterostructure can have,for example, a cladding layer 72 or passivation layer completely or atleast partially surrounding an active photoluminescent layer 74. Thecladding layer 72 can have a bandgap larger than the bandgap of theactive photoluminescent layer 74. In an embodiment, the bandgap energyof the active photoluminescent layer 74 is lower than the bandgap energyof the first light emitter 10 and the bandgap energy of the claddinglayer 72 is higher than the bandgap energy of the first light emitter 10so that the first light 60 emitted by the first light emitter 10 isconverted into emitted second light 62 by the photoluminescent layer 74and not the cladding layer 72. In another embodiment, the bandgap energyof the cladding layer 72 is not higher than the bandgap energy of thefirst light emitter 10 but is sufficiently thin that relatively littleof the first light 60 emitted by the first light emitter 10 is convertedinto emitted second light 62 by the cladding layer 72, for example thecladding layer 72 is thinner than the photoluminescent layer 74 as shownin FIG. 11. Such a heterostructure improves the efficiency of lightemission.

The cladding layer 72 or passivation layer increases color-conversionefficiency by suppressing non-radiative recombination of photo-generatedelectrons and holes at the free surfaces of the second light emitter 20.Free surfaces of the second light emitter 20 can contribute tonon-radiative recombination (a parasitic effect) due to the presence ofsurface states, traps, and/or surface contamination. Cladding layers 72or passivation layers reduce or eliminate the effects of one or more ofthose sources of non-radiative recombination. Some passivation layers(e.g., some dielectric materials deposited by atomic layer depositionwith in-situ passivation immediately prior to growth) suppressnon-radiative recombination by reducing or eliminating the density ofinterface states at the interfaces between the photoluminescentmaterials and the passivation materials. Some passivation layers, suchas higher-bandgap semiconductor cladding layers 72, reduce non-radiativerecombination by forming electrostatic barriers that keepphoto-generated carriers from traversing the interface between thephotoluminescent material and the cladding material.

Core-shell nanoparticles are known as color-conversion materials thatare more efficient than nano-particles without a cladding “shell.” Manyclasses of electronic or optoelectronic devices (e.g., yield-effecttransistors or solar cells) rely on surface passivation for efficientoperation. Embodiments of the present invention applysurface-passivation strategies to the color-conversion structures of thepresent invention described herein.

A cladding layer 72 can be on one, some, or all sides of the secondlight emitter 20. In one embodiment, a cladding layer 72 is a planarepitaxial layer that has a bandgap energy higher than the bandgap energyof the photo-luminescent layer 74. In one embodiment the cladding layer72 is InGaAlP, and the photo-luminescent layer is InGaP. In oneembodiment the cladding layer 72 is InAlGaN, AlGaN, or InGaN having ahigher bandgap than the photo-luminescent layer, and thephoto-luminescent layer is InGaN having a lower bandgap than thecladding layer 72. In one embodiment, a cladding layer 72 is anepitaxial layer grown on the sidewalls and tops of mesas of aphotoluminescent layer 74 as an epitaxial “overgrowth” (“overgrowth”refers to the second epitaxial process in the following sequence: formepitaxial materials in a first epitaxial process, do photolithographyand etching or other micro-fabrication processes, then form moreepitaxial materials in a second epitaxial (overgrowth) process). In someembodiments the tops and bottoms of the second light emitters 20 havecladding layers 72 and the sidewalls have no cladding or otherpassivation.

In some embodiments the tops and bottoms of the second light emitters 20have cladding layers formed by epitaxial deposition processes and thesidewalls have passivation formed by atomic layer deposition or otherchemical vapor deposition. In some embodiments all sides of the secondlight emitters 20 are passivated by hetero-epitaxial cladding layers 72.

In some embodiments one or more surfaces of the second light emitter 20are passivated by ion processing. In an embodiment ion processing altersthe electron- or hole-transport properties near one or more surfaces ofthe second light emitter 20 (e.g. the sidewalls) and inhibitstrap-assisted non-radiative recombination there.

A method of the present invention is illustrated in the flow chart ofFIG. 12. In step 100 a display substrate 30 is provided, in step 105first light emitters 10 such as micro-LEDs are provided, and in step 102color-conversion crystals are provided. The display substrate 30, insome embodiments, is a polymer, plastic, resin, polyimide, PEN, PET,metal, metal foil, glass. The first light emitters 10 can be smallinorganic light-emitting diodes or micro-LEDs. A discussion ofmicro-LEDs and micro-LED displays can be found in U.S. patentapplication Ser. No. 14/743,981, filed Jun. 18, 2015, entitled MicroAssembled Micro LED Displays and Lighting Elements, which is herebyincorporated by reference in its entirety. The display substrate 30,micro-LED first light emitters 10, and color-conversion crystal secondlight emitters 20 can all be provided at the same or at different timesand in any order.

Conductive wires 18 are formed on the display substrate 30 in step 110and the micro-LED first light emitters 10 are located on the displaysubstrate 30 in alignment with the conductive wires 18 in step 120, forexample by micro-transfer printing. The color-conversion crystals arethen located on the display substrate 30 within 0 to 250 microns of themicro-LEDs, in step 130, for example by micro-transfer printing thecolor-conversion crystals onto the micro-LEDs. This method can form atop-emitter structure, such as is shown in FIG. 6. Micro-transfermethods are described in U.S. Pat. Nos. 8,722,458, 7,622,367 and8,506,867, each of which is hereby incorporated by reference.

Alternatively, referring to the method of the present inventionillustrated in the flow chart of FIG. 13, the step 130 of locating thecolor-conversion crystals is reversed with the step 120 of locating, forexample by micro-transfer printing, the micro-LEDs and the step 110 offorming conductive wires 18 to electrically interconnect the micro-LEDsis performed after the micro-LEDs are located on the display substrate30. This method can form a bottom-emitter structure, such as is shown inFIG. 2.

In another embodiment of the present invention, the first light emitters10 are micro transfer printed onto the second light emitters 20 to forma light-emitting crystalline color-conversion structure 5. Thecrystalline color-conversion structure 5 is then micro-transfer printedonto a display substrate 30.

In an embodiment, a source substrate is provided, for example asemiconductor substrate that is an inorganic solid single-crystaldirect-bandgap source substrate. The first light emitters 10 are microtransfer printed onto the source substrate, forming light-emittingcrystalline color-conversion structures 5, and then the light-emittingcrystalline color-conversion structures 5 are released from the sourcesubstrate, together with a portion of the source substrate forming thesecond light emitters 20 and micro transfer printed from the sourcesubstrate to a destination substrate, such as the display substrate 30.Structures useful for micro transfer printing, for example releaselayers, anchors, and tethers, can be formed in the source substratebefore or after the first light emitters 10 are micro transfer printedonto the source substrate.

In an alternative embodiment, an inorganic solid single-crystaldirect-bandgap layer is formed on a source substrate and the first lightemitters 10 are disposed, for example by micro transfer printing, ontothe layer, forming spatially separated light-emitting crystallinecolor-conversion structures 5 on the source substrate, and then thelight-emitting crystalline color-conversion structures 5 are releasedfrom the source substrate and printed onto a destination substrate, suchas the display substrate 30. Structures useful for micro transferprinting, for example release layers, anchors, and tethers, can beformed in the source substrate before or after the first light emitters10 are micro transfer printed onto the source substrate 30.

In general, structures, features, and elements of the present inventioncan be made using photolithographic methods and materials found in theintegrated circuit arts, the light-emitting diode arts, and the laserarts, for example including doped or undoped semiconductor materials,optically pumped crystals, conductors, passivation layer, electricalcontacts, and controllers.

In another embodiment, the crystalline color-conversion devices 5 arearranged on tile substrates that are then mounted on and interconnectedto a backplane substrate to form a compound micro-assembly. Depending onthe implementation, different number of crystalline color-conversiondevices 5 are located on each tile substrate and interconnected. Invarious embodiments, control circuitry is located on the tile substratesor the backplane substrate. A discussion of compound micro-assemblystructures and methods is provided in U.S. patent application Ser. No.14/822,868 filed Aug. 10, 2015, entitled Compound Micro-AssemblyStrategies and Devices, which is hereby incorporated by reference in itsentirety.

As is understood by those skilled in the art, the terms “over” and“under” are relative terms and can be interchanged in reference todifferent orientations of the layers, elements, and substrates includedin the present invention. For example, a first layer on a second layer,in some implementations means a first layer directly on and in contactwith a second layer. In other implementations a first layer on a secondlayer includes a first layer and a second layer with another layer therebetween.

Having described certain implementations of embodiments, it will nowbecome apparent to one of skill in the art that other implementationsincorporating the concepts of the disclosure may be used. Therefore, theinvention should not be limited to the described embodiment, but rathershould be limited only by the spirit and scope of the following claims.

Throughout the description, where apparatus and systems are described ashaving, including, or comprising specific components, or where processesand methods are described as having, including, or comprising specificsteps, it is contemplated that, additionally, there are apparatus, andsystems of the disclosed technology that consist essentially of, orconsist of, the recited components, and that there are processes andmethods according to the disclosed technology that consist essentiallyof, or consist of, the recited processing steps.

It should be understood that the order of steps or order for performingcertain action is immaterial so long as the disclosed technology remainsoperable. Moreover, two or more steps or actions in some circumstancescan be conducted simultaneously. The invention has been described indetail with particular reference to certain embodiments thereof, but itwill be understood that variations and modifications can be effectedwithin the spirit and scope of the invention.

PARTS LIST

-   T1 first thickness-   T2 second thickness-   5 crystalline color-conversion device-   5R crystalline color-conversion device-   5G crystalline color-conversion device-   5B crystalline color-conversion device-   7 crystalline color-conversion display-   10 first light emitter-   11 light-emitting area-   12 light-emitting layer-   13 conduction layer-   14 electrical contact-   15 reflector-   16 dielectric insulator-   17 electrostatic gate-   18 conductive wire-   20 second light emitter-   22 material-   28 third light emitter-   30 substrate/display substrate-   40 group/pixel group-   60 first light-   61 low-energy pump light-   62 second light-   62A second light-   62B second light-   64A third light-   64B third light-   70 semiconductor heterostructure-   72 cladding layer-   74 active luminescent layer-   100 provide display substrate step-   102 provide color-conversion crystals step-   105 provide light emitters step-   110 form wires on substrate step-   120 print micro-LEDs on display substrate step-   130 locate color-conversion crystals on micro-LEDs step

1. A crystalline color-conversion device, comprising: an electrically driven first light emitter for emitting first light having a first energy in response to an electrical signal; and an inorganic solid single-crystal direct-bandgap second light emitter having a bandgap of a second energy less than the first energy, wherein the second light emitter is electrically isolated from the first light emitter, is located in optical association with the first light emitter, and is located within 0 to 250 microns of the first light emitter so that in response to the electrical signal the first light emitter emits first light that is absorbed by the second light emitter and the second light emitter emits second light having a lower energy than the first energy. 2-5. (canceled)
 6. The crystalline color-conversion device of claim 1, wherein the first light emitter is in physical contact with the second light emitter.
 7. The crystalline color-conversion device of claim 1, comprising a material that is at least partially transparent to the color of light emitted by the first light emitter and is located between and in contact with the first light emitter and the second light emitter.
 8. The crystalline color-conversion device of claim 7, wherein the material is plastic, is an adhesive, is a curable adhesive, is a resin, or is a curable resin, or wherein the material is a dielectric stack that is an optical filter. 9-14. (canceled)
 15. The crystalline color-conversion device of claim 14, wherein at least one of the plurality of second light emitters emits second light that is red, green, blue, or infrared.
 16. The crystalline color-conversion device of claim 15, wherein at least a first one of the plurality of second light emitters emits red light, a second one of the plurality of second light emitters emits green light, and a third one of the plurality of second light emitters emits blue light.
 17. The crystalline color-conversion device of claim 1, wherein the first light emitter emits white light.
 18. The crystalline color-conversion device of claim 1, wherein the first light emitter emits a third light of a third energy less than the second energy and the third light passes through the second light emitter. 19-20. (canceled)
 21. The crystalline color-conversion device of claim 1, wherein the second light emitter has a thickness chosen to convert a pre-determined fraction of the incident first light having an energy greater than the second energy to light of the second energy.
 22. The crystalline color-conversion device of claim 21, comprising an inorganic solid single-crystal direct-bandgap third light emitter having a bandgap of a third energy less than the first energy, the third light emitter located on a side of the second light emitter opposite the first light emitter.
 23. The crystalline color-conversion device of claim 1, wherein the second light emitter has at least a first portion having a first thickness and a second portion having a second thickness less than the first thickness, the first thickness large enough to convert substantially all incident first light having an energy greater than the second energy to light of the second energy and the second thickness small enough that a substantial amount of incident first light having an energy greater than the second energy is not converted to light of the second energy.
 24. The crystalline color-conversion device of claim 1, wherein the second light emitter comprises a cavity in which the first light emitter is disposed. 25-26. (canceled)
 27. The crystalline color-conversion device of claim 1, comprising an inorganic solid single-crystal direct-bandgap third light emitter having a bandgap of a third energy less than the first energy and that is electrically isolated from the first light emitter.
 28. The crystalline color-conversion device of claim 27, wherein the third light emitter is located in optical association with the first light emitter and is located within 0 to 250 microns of the first light emitter so that in response to the electrical signal the first light emitter emits first light that is absorbed by the third light emitter and the third light emitter emits third light having a lower energy than the first energy.
 29. The crystalline color-conversion device of claim 27, wherein the third light emitter has a bandgap of a third energy less than the second energy, the third light emitter is located in optical association with the second light emitter, and is located within 0 to 250 microns of the second light emitter so that light emitted by the second light emitter is absorbed by the third light emitter and the third light emitter emits third light having a lower energy than the second energy.
 30. The crystalline color-conversion device of claim 1, comprising a reflective layer located at least partially over the first light emitter or the second light emitter, or both the first light emitter and the second light emitter, that reflects light emitted by the first or second light emitters in undesirable directions. 31-41. (canceled)
 42. The crystalline color-conversion device of claim 1, comprising an optical filter disposed on a side of the second light emitter opposite the first light emitter to reflect light from the first light emitter and transmit light emitted from the second light emitter.
 43. A crystalline color-conversion display, comprising: a display substrate; the plurality of first light emitters and corresponding plurality of second light emitters according to claim 11 located on or over the display substrate and distributed over the display substrate. 44-45. (canceled)
 46. The crystalline color-conversion display of claim 1, wherein the second light emitters are located between the first light emitters and the display substrate and the second light emitters emit light through the display substrate.
 47. The crystalline color-conversion display of claim 1, wherein the first light emitters are located between the second light emitters and the display substrate and the second light emitters emit light in a direction opposite the display substrate. 48-49. (canceled)
 50. A method of making a crystalline color-conversion device, comprising: providing an electrically driven first light emitter for emitting first light having a first energy in response to an electrical signal; providing an inorganic solid single-crystal direct-bandgap second light emitter having a bandgap of a second energy less than the first energy; and micro transfer printing the second light emitter onto the first light emitter or micro transfer printing the first light emitter onto the second light emitter, wherein the second light emitter is electrically isolated from the first light emitter, is located in optical association with the first light emitter, and is located within 0 to 250 microns of the first light emitter so that in response to the electrical signal the first light emitter emits first light that is absorbed by the second light emitter and the second light emitter emits second light having a lower energy than the first energy. 51-57. (canceled) 